240 watts of LED backlight for a 23″ computer monitor!

Posted Oct 13, 2012 by Homebrew

[This is a very old article from scanning backlight experiments in 2012]

A 23″ LCD computer monitor is 286mm high x 508mm wide. From math calculations on LED ribbons (120 LED per meter, 6mm wide, 6500K, ~10watt/meter, 80+CRI available), one can put 48 rows of 6mm-width ribbon segments behind a 23″ LCD. That’s a whopping 240 watts of backlight for a 23″ computer monitor!  

This will allow 90% motion blur reduction using ultra-short scanning backlight strobes (see FAQ) without a dim picture, 1.6ms strobes at 60Hz, resulting in 24 watt average actual power consumption. Many new 23″ LCD monitors with a LED backlight, adjusted to a comfortable brightness, consume just about 15-20 watts for the backlight itself. I will have brightness left over to go to 95% motion blur reduction, using 0.8ms strobes at 60Hz native refresh (simulating equivalence to 960Hz), or 0.4ms strobes at 120Hz native refresh (simulating equivalence to 1920Hz).

LED ribbons are cheap (search eBay, Alibaba, Google for “LED ribbon”). If you know another inexpensive alternatives of putting nearly 300 watt of backlight behind a 23″ monitor, contact mark[at]scanningbacklight.com

About Mark Rejhon

Also known as Chief Blur Buster. Founder of Blur Busters. Inventor of TestUFO. Read more about him on the About Mark page.

4 Comments For “240 watts of LED backlight for a 23″ computer monitor!”

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MrInvisible3
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MrInvisible3

The correct grid or checkerboard layout of LED’s will be important for easiest backlight diffusion. #5050 LED ribbons at 60 LEDs/meter have a 16mm LED pitch. The ribbons are 10mm wide, placed edge-to-edge as tightly as possible behind an LCD panel.

Putting #5050 LED’s in a checkerboard pattern (offsetting every other row of ribbon horizontally by 8mm) will produce much more even backlight diffusion than aligning in a grid pattern due to the bigger difference in horizontal versus vertical pitch (16mm horizontal pitch, 10mm vertical pitch) in the grid layout.

I am avoiding the waterproof ribbons. The transparent plastic casing thickens the ribbon, to at least 12mm. Besides, a computer monitor normally doesn’t need to be made waterproof, anyway.

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12 years 1 month ago
MrInvisible3
Member
MrInvisible3

I have done some more research, and consultations with LED ribbon suppliers.

I have come to the conclusion that #5050 LED’s may be a better bet. The ribbons with #5050 LED’s are much brighter, but the ribbons are wider at 10mm and there are only 60 LED’s per meter. However, the better inexpensive ribbons use 14.4 watts per meter, using high-efficiency white 6000K 70 CRI Epistar LED’s (21-22 lumens per LED, for high quality $7/meter ribbon). This is adequate color quality for a backlight, if the goal is motion blur elimination more so than photo image quality.

For this #5050 LED ribbon, tightly packing 30 rows of 0.5 meter ribbons behind a 23″ monitor, leads to 216 watts of backlight, 900 LED’s, and almost a whopping 20,000 lumens! With a slight overvoltage during short pulse operation (LED’s permit higher peak currents if strobed), more than 40,000+ lumens is possible in a 23″ computer monitor backlight. This amount of lumens is sufficient to make a 23″ LCD to have less motion blur than a CRT.

The more lumens, the merrier. Strobes need to be as short and as bright as a CRT phosphor illumination (CRT phosphors output an incredible amount of light over a tiny time period!) — for scientifically proper motion blur elimination using a scanning backlight, my scanning backlight needs to closely emulate a CRT in this high-speed video: http://marky.com/backlight/crt-comparison/ — look at how bright the phosphor is for a tiny time period: Over an order of magnitude brighter than a regular LCD backlight.

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12 years 1 month ago
MrInvisible3
Member
MrInvisible3

The math is as follows:

Typical sizes of computer monitors:
23″ computer display = 11.25″ x 20.00″ = 286mm high x 508mm wide.
27″ computer display = 13.24″ x 23.54″ = 337mm high x 598mm wide.

For 8 millimeter wide ribbons
….. 36 ribbon pieces edge-to-edge behind a 23″ display (286mm divided by 8mm)
….. 43 ribbon pieces edge-to-edge behind a 27″ display (337mm divided by 8mm)
Total ribbon wattage is 180watt for 23″, or 258watt for 27″

For 6 millimeter wide ribbons
….. 48 ribbon pieces edge-to-edge behind a 23″ display (286mm divided by 6mm)
….. 56 ribbon pieces edge-to-edge behind a 27″ display (337mm divided by 6mm)
Total ribbon wattage is 240watt for 23″ or 336watt for 27″

Common LED ribbons are available in various number of LED’s per meter, going up to 120 LED’s per meter (600 LED per 5 meter reel, 10 watts per meter). Ribbons are cuttable at intervals. Various color temperatures are available, and backlight-quality LED chips are available (6500K, 80+ CRI). Ribbon widths come in either 6mm or 8mm for ribbons that use #3528 surface mounted LED chips. There are ribbons that use #5050 LED chips and other sizes, but are wider (12mm). Even though #5050 is brighter, you can squeeze three to four times as many #3528 LED’s in the same square footage, and the evenness of the backlight will be better, especially when trying to keep a full-array backlight in a very thin display.

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12 years 1 month ago
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